Intermetallic compound superconducting material comprising magnesium and beryllium and alloy superconducting material containing the intermetallic compound and method for preparing the same

ABSTRACT

There are provided an intermetallic-compound superconductor that is high in superconducting transition temperature, and an alloy superconductor that is high in superconducting transition temperature and excels in malleability and ductility, as well as a method of making such a superconductor with good reproducibility and at a low cost of manufacture. This entirely new intermetallic compound superconductor is made of magnesium (Mg) and beryllium (Be) and has a chemical composition expressed by formula: Mg 1 Be 2 , has a hexagonal AlB 2  type crystallographic structure and has a superconducting transition temperature (T c ) of 35 K. An alloy containing this intermetallic compound excels in malleability and ductility and constitutes the alloy superconductor having a superconducting transition temperature (T c ) of 35 K and being low in specific resistance for normal conduction at a temperature ranging from the superconducting transition temperature to a room temperature. In the method of manufacture, a Mg containing feedstock powder and a Be containing feedstock powder are mixed together to form a mixture thereof which is, e.g., hot pressed to produce a semiconductor product.

TECHNICAL FIELD

[0001] This present invention relates to an intermetallic-compoundsuperconductor and an alloy superconductor which can be utilized insuperconducting electronics such as a large scale electric powertransmission system, a superconductive power storage system, a highperformance Josephson device and a high frequency electronic device, andwhich especially are high in superconducting transition temperature, areeasy to manufacture, excel in malleability and ductility, and yet arealtogether new. The invention also relates to a method of making such anovel superconductor.

BACKGROUND ART

[0002] Superconductors are known to include a superconductor made of asimple metal, a superconductor made of a compound, and a superconductormade of composite oxides.

[0003] A simple metal superconductor may contain a simple metal such asPb and Nb but is known to lack utility because it is low insuperconducting transition temperature.

[0004] Known as intermetallic compound superconductors include thosehaving a A15 type crystallographic structure of intermetallic compoundsas represented by Nb₃Ge, Nb₃Ga, Nb₃AI and Nb₃Sn, and those having achevrel type crystallographic structure of intermetallic compounds asrepresented by PbMo₆S₈. Intermetallic compound superconductors having anAIB₂ type crystallographic structure of intermetallic compounds asrepresented by NbB₂ are also known which, however, are also known to beextremely low in superconducting transition temperature (T_(c)=0.62 K,see Journal of the Less-Common Metals, 67 (1979), 249-255). Theseintermetallic compound superconductors include one with Nb₃Ge which isrelatively high in superconducting transition temperature (=about 23 K),but commonly have the disadvantage that they are weak in distortion andare fragile.

[0005] Known as a composite oxide superconductor include La group oxidesuperconductors as represented by composition La_(2-x)Ba_(x)CuO₄, Ygroup oxide superconductors as represented by compositionY₁Ba₂Cu₃O_(7-x), Bi group oxide superconductors as represented bycomposition Bi₂Sr₂C_(n-1)Cu_(n)O_(2n+2), Tl group superconductors asrepresented by composition Tl₂Ba₂Ca_(n-1)Cu_(n)O_(2n+2), and Hg groupoxide superconductors as represented by Hg₁Ba₁CaCu₁O_(6+x). Thesecomposite oxide superconductors are high in superconducting transitiontemperature and indeed include those which have their superconductingtransition temperatures reaching as high as 150 K. The composite oxidesuperconductor has a perovskite structure made up of a lamination of anoctahedral, pyramidal or planar superconducting layer of CuO₂, and ablock layer (dissimilar in crystallographic structure to thesuperconducting layer) made of an atom or atoms such as La, Ca, Y, Bi orHg and oxygen. As such the extreme complexity of the crystallographicstructure of a composite oxide superconductor makes it difficult toconduct its production in a large volume and with good reproducibly. Inaddition, the superconductor being a composite oxide is naturally poorin both malleability and ductility, and is hard to use as asuperconducting electric cable or wire.

[0006] A well known alloy superconductor is a Nb—Ti alloy, which isexcellent in malleability and ductility and hence has been used to formsuperconducting electric cables or wires and superconducting magnets.However, an alloy conductor is as low in superconducting transitiontemperature as, e.g., about 9 K with the Nb—Ti alloy, and henceimprovements in them are being sought.

[0007] As to superconducting cables or wires, it should also be notedthat it may happen that a portion of a superconducting cableincidentally becomes normally conductive. Once this takes place, it maybring about a phenomenon, known as the “quenching” phenomenon, thattriggered by Joule heating of the portion rendered normally conductiveto have a finite electrical resistance, the entire material in a momentbecomes normally conductive. When the quenching phenomenon occurs,serious consequences are met such as the burning of the superconductingcable and the explosive vaporization of coolant, both due to the Jouleheat.

[0008] An attempt that has so far been made to avoid the quenchingphenomenon is to provide a current bypass for a superconducting cable bywinding a metal wire low in electric resistivity (specific resistance)around the superconducting cable so that when a portion of thesuperconducting cables incidentally becomes normally conductive, thecurrent is allowed to escape through the current bypass.

[0009] The metal wire low in electric resistivity must, however, beformed of a metal such as silver (Ag) that is expensive and musttherefore make the superconducting cable costly.

[0010] It is accordingly an object of the present invention to providean intermetallic-compound superconductor that is high in superconductingtransition temperature and an alloy superconductor that is high insuperconducting transition temperature and also excels in malleabilityand ductility, and that can be used to form a superconducting cablewithout the need for a current bypassing metal wire. It is further anobject of the present invention to provide methods of making thesesuperconductors reproducibly and at a relative low cost of manufacture.

DISCLOSURE OF THE INVENTION

[0011] In order to attain the object first mentioned above, there isprovided in accordance with the present invention anintermetallic-compound superconductor characterized in that it is madeof magnesium (Mg) and beryllium (Be).

[0012] The object first mentioned above is also attained in accordancewith the present invention by an alloy superconductor characterized inthat it contains an intermetallic compound made of Mg and Be and alsocontains one or more metallic elements.

[0013] The said intermetallic-compound superconductor preferably has acomposition represented by chemical composition formula: Mg₁Be₂ andhaving a hexagonal AlB₂ type crystallographic structure in which a Mglayer and a Be layer alternately lie.

[0014] Also, the said alloy superconductor that contains anintermetallic compound made of Mg and Be when it also contains oneadditional element may contains B as the one additional element; then itis characterized in that it is an alloy having a composition representedby composition formula: MgBe_(x)B_(y) where 0<x<20 and 0<y<20.

[0015] The said intermetallic-compound superconductor preferably has asuperconducting transition temperature (T_(c)) of 35 K.

[0016] The said alloy superconductor preferably has a superconductingtransition temperature (T_(c)) of 35 K.

[0017] The said intermetallic-compound superconductor preferably has aspecific resistance not greater than 6×10⁻⁵ ohm-cm at a temperatureranging from its superconducting transition temperature (T_(c)) of 35 Kto a room temperature.

[0018] The said alloy superconductor preferably has a specificresistance not greater than 6×10⁻⁵ ohm-cm at a temperature ranging fromits superconducting transition temperature (T_(c)) of 35 K to a roomtemperature.

[0019] The intermetallic compound superconductor made up as mentionedabove has a superconducting transition temperature (T_(c)) of 35 K, andis higher in superconducting transition temperature than anyintermetallic compound superconductor so far known and indeed muchhigher in superconducting transition temperature than any knownintermetallic compound superconductor having the AlB₂ typecrystallographic structure. Moreover, it is lower in specific resistanceat a temperature ranging from the superconducting transition temperatureto a room temperature than any intermetallic-compound superconductor sofar known.

[0020] Also, the alloy superconductor made up as mentioned above has asuperconducting transition temperature (T_(c)) of 35 K, and is higher insuperconducting transition temperature than any alloy superconductor sofar known and also excels in both malleability and ductility. Moreover,it is lower in specific resistance at a temperature ranging from thesuperconducting transition temperature to a room temperature than anyalloy superconductor so far known.

[0021] The intermetallic-compound superconductor made up as mentionedabove can be used as a superconductor high in superconducting transitiontemperature (T_(c)) in superconducting electronics such as a highperformance Josephson device and a high frequency or electronic device.

[0022] Further, the alloy superconductor containing the intermetalliccompound made up as mentioned above can be used as a superconductor highin superconducting transition temperature and also excellent inmalleability and ductility for a superconducting electric wire or cableused in a superconducting electric power transmission system, asuperconducting electric power storage system or the like and also in asuperconducting electronic component such as a high performanceJosephson device and a high frequency or electronic device.

[0023] The present invention further provides a method of making anintermetallic compound superconductor, which method is characterized inthat it comprises the steps of: mixing a Mg containing feedstock powderand a Be containing feedstock powder together to form a mixture powderthereof so that the mixture powder contains Mg and Be at a compositionalratio of Mg/Be=1/2, shaping the said mixture powder into the form of apellet, and heating the said pellet in an inert gas to form theintermetallic compound superconductor.

[0024] An alternative method of manufacture of an intermetallic compoundsuperconductor in accordance with the present invention may comprise thesteps of: mixing a Mg containing feedstock powder and a Be containingfeedstock powder together to form a mixture powder thereof so that themixture powder contains Mg and Be at a compositional ratio of Mg/Be=1/2,shaping the said mixture powder into the form of a pellet, and heatingthe said pellet in a vacuum to form the intermetallic compoundsuperconductor.

[0025] An alternative method of manufacture of an intermetallic compoundsuperconductor in accordance with the present invention may comprise thesteps of: mixing a Mg containing feedstock powder and a Be containingfeedstock powder together to form a mixture powder thereof so that themixture powder contains Mg and Be at a compositional ratio of Mg/Be=1/2,shaping the said mixture powder into the form of a pellet, and heatingthe said pellet in a pressurized inert gas to form the intermetalliccompound superconductor.

[0026] An alternative method of manufacture of an intermetallic compoundsuperconductor in accordance with the present invention may comprise thesteps of: mixing a Mg containing feedstock powder and a Be containingfeedstock powder together to form a mixture powder thereof so that themixture powder contains Mg and Be at a compositional ratio of Mg/Be=1/2,shaping the said mixture powder into the form of a pellet, and pressingand heating or hot-pressing the said pellet to form the intermetalliccompound superconductor.

[0027] The present invention also provides a method of making an alloysuperconductor, characterized in that it comprises the steps of: mixinga Mg containing feedstock powder, a Be containing feedstock powder and aB containing powder together to form a mixture powder thereof so thatthe mixture powder contains Mg, Be and B at a compositional ratio ofMg:Be:B=1:x:y where 0<x<20 and 0<y<20, shaping the said mixture powderinto the form of a pellet, and heating the said pellet in an inert gasto form the alloy superconductor.

[0028] An alternative method of manufacture of an alloy superconductorin accordance with the present invention may comprise the steps of:mixing a Mg containing feedstock powder, a Be containing feedstockpowder and a B containing feedstock powder together to form a mixturepowder thereof so that the mixture powder contains Mg, Be and B at acompositional ratio of Mg:Be:B=1:x:y where 0<x<20 and 0<y<20, shapingthe said mixture powder into the form of a pellet, and heating the saidpellet in a vacuum to form the alloy superconductor.

[0029] An alternative method of manufacture of an alloy superconductorin accordance with the present invention may comprise the steps of:mixing a Mg containing feedstock powder, a Be containing feedstockpowder and a B containing feedstock powder together to form a mixturepowder thereof so that the mixture powder contains Mg, Be and B at acompositional ratio of Mg:Be:B=1:x:y where 0<x<20 and 0<y<20, shapingthe said mixture powder into the form of a pellet, and heating the saidpellet in a pressurized inert gas as an alternative to the vacuum orinert gas to form the alloy superconductor.

[0030] An alternative method of manufacture of an alloy superconductorin accordance with the present invention may comprise the steps of:mixing a Mg containing powder, a Be containing feedstock powder and a Bcontaining feedstock powder together to form a mixture powder thereof sothat the mixture powder contains Mg, Be and B at a compositional ratioof Mg:Be:B=1:x:y where 0<x<20 and 0<y<20, shaping the said mixturepowder into the form of a pellet, and pressing and heating or hotpressing the said pellet to form the alloy superconductor.

[0031] In the method of manufacture of an intermetallic-compoundsuperconductor mentioned above, the said pellet is preferably heated inthe said inert gas at a temperature of 700 to 2000° C. for a period ofseveral seconds or more.

[0032] In the method of manufacture of an intermetallic compoundsuperconductor mentioned above, the said pellet is preferably heated inthe vacuum under a pressure of 2×10⁻² Pa or less at a temperature of 650to 1100° C. for a period of several minutes or more.

[0033] In the method of manufacture of an intermetallic compoundsuperconductor mentioned above, the said pellet is also preferablyheated in the said inert gas under a pressure of 1 to 200 MPa at atemperature of 600 to 1100° C. for a period of several minutes or more.

[0034] In the method of manufacture of an intermetallic compoundsuperconductor mentioned above, the said pellet is also preferablypressed and heated or hot pressed under a pressure of 0.1 to 6 GPa at atemperature of 700 to 1400° C. for a period of several minutes or more.

[0035] In the method of manufacture of an alloy superconductor mentionedabove, the said pellet is advantageously heated in the said inert gas ata temperature of 700 to 2000° C. for a period of several seconds ormore.

[0036] In the method of manufacture of an alloy superconductor mentionedabove, the said pellet is advantageously heated in the vacuum under apressure of 2×10⁻² Pa or less at a temperature of 650 to 1100° C. for aperiod of several minutes or more.

[0037] In the method of manufacture of an alloy superconductor mentionedabove, the said pellet is advantageously heated in the said inert gasalso under a pressure of 1 to 200 MPa at a temperature of 600 to 1100°C. for a period of several minutes or more.

[0038] In the method of manufacture of an alloy superconductor mentionedabove, the said pellet is advantageously pressed and heated or hotpressed under a pressure of 0.1 to 6 GPa at a temperature of 700 to1400° C. for a period of several minutes or more.

[0039] The methods of making an intermetallic compound superconductormentioned above permit an intermetallic-compound superconductor composedof magnesium (Mg) and beryllium (Be) in accordance with the presentinvention to be manufactured reproducibly and easily.

[0040] The methods mentioned above of making an alloy superconductorcontaining an intermetallic compound permit an alloy superconductorcontaining an intermetallic compound in accordance with the presentinvention to be manufactured reproducibly and easily.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention will better be understood from thefollowing detailed description and the drawings attached hereto showingcertain illustrative forms of embodiment of the present invention. Inthis connection, it should be noted that such forms of embodimentillustrated in the accompanying drawings hereof are intended in no wayto limit the present invention but to facilitate an explanation andunderstanding thereof. In the drawings:

[0042]FIG. 1 is a diagram illustrating a result of powder X-raydiffraction measurements conducted of an alloy superconductor of acomposition represented by composition formula: Mg₁Be_(x)B_(y) (where0<x<20 and 0<y<20) according to the present invention;

[0043]FIG. 2 is a diagram illustrating a result of measurementsconducted to derive the temperature characteristics of the electricalresistivity of an alloy superconductor of a composition represented bycomposition formula: Mg₁Be_(x)B_(y) (where 0<x<20 and 0<y<20) accordingto the present invention; and

[0044]FIG. 3 is a diagram illustrating a result of measurementsconducted to derive the temperature characteristics of the magneticsusceptibility of an alloy superconductor of a composition representedby composition formula: Mg₁Be_(x)B_(y) (where 0<x<20 and 0<y<20)according to the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

[0045] Hereinafter, the present invention will be described in detailwith reference to suitable forms of implementation thereof illustratedin the drawing figures.

[0046] Mention is first made of the crystallographic structure of analloy superconductor that contains an intermetallic compound made ofmagnesium (Mg) and beryllium (Be) according to the present invention andalso contains boron (B) as one additional element also in accordancewith the present invention.

[0047]FIG. 1 is a diagram illustrating a result of powder X-raydiffraction measurements conducted of an alloy superconductor of acomposition represented by composition formula: Mg₁Be_(x)B_(y) (where0<x<20 and 0<y<20) according to the present invention.

[0048] The X-ray diffraction measurements were conducted using a biaxialX-ray diffraction analyzer (made by company RIGAKU, model RINT2000).

[0049] From the powder X-ray diffraction measurement pattern shown inFIG. 1, it is seen that the alloy superconductor of the presentinvention has a crystallographic structure that is hexagonal and belongsto the space group p6/mmm. It is also seen that with its a-axis having alength of 3.084 angstroms and its c-axis having a length of 3.5508angstroms, it is a hexagonal AlB₂ type crystallographic structure.

[0050] Also in identifying the chemical composition of anintermetallic-compound superconductor according to the presentinvention, use is made of EPMA (Electron Probe Micro Analysis) and ICP(Induced Coupled Plasma) methods.

[0051] Mention is next made of the superconducting characteristics of analloy superconductor of an alloy superconductor of a compositionrepresented by composition formula: Mg₁Be_(x)B_(y) (where 0<x<20 and0<y<20) according to the present invention.

[0052]FIG. 2 is a diagram illustrating a result of measurementsconducted to derive the temperature characteristics of the specificresistance (electrical resistivity) of an alloy superconductor of acomposition represented by composition formula: Mg₁Be_(x)B_(y) (where0<x<20 and 0<y<20) according to the present invention. The electricalresistance was measured according to the 4-probe method.

[0053] From FIG. 2, it is seen that the electrical resistance decreaseswith the temperature decreased, and sharply becomes zero at atemperature of 35 K, which indicates that the intermetallic compound hasa superconducting transition temperature of 35 K. It is also seen fromFIG. 2 that its specific resistance for normal conduction is extremelyas low as 6×10⁻⁵ ohm-cm over a temperature range from thesuperconducting transition temperature of 35 K to a room temperature.

[0054] Mention is next made of a result of measurements of the magneticsusceptibility of an alloy superconductor of a composition representedby composition formula: Mg₁Be_(x)B_(y) (where 0<x<20 and 0<y<20)according to the present invention.

[0055]FIG. 3 is a diagram illustrating a result of measurementsconducted to derive the temperature characteristics of the magneticsusceptibility of an alloy superconductor of a composition representedby composition formula: Mg₁Be_(x)B_(y) (where 0<x<20 and 0<y<20)according to the present invention. The magnetic susceptibilities weremeasured using a DC susceptometer or DC susceptibility measurementapparatus (made by company Quantum Design, MPMS Series, Model MPMS-R2).

[0056] As is apparent from FIG. 3, exhibiting negative susceptibilities,namely diamagnetism, at temperatures lower than T_(c)=35 K it is seenthat the alloy superconductor of a composition represented bycomposition formula: Mg₁Be_(x)B_(y) (where 0<x<20 and 0<y<20) accordingto the present invention is a superconductor having a superconductingtransition temperature of T_(c)=35 K.

[0057] Mention is next made of methods of making anintermetallic-compound superconductor made of magnesium and beryllium,and an alloy superconductor containing the intermetallic compound madeof magnesium and beryllium and also boron as its one additional metallicelement, in accordance with the present invention.

[0058] In the methods of making according to the present invention to bedescribed below, if feedstock powders are mixed together to contain Mgand Be at a compositional ratio of Mg/Be=1/2, then there is formed asingle phase intermetallic compound superconductor of the hexagonal AlB₂type crystallographic structure expressed by composition formula:Mg₁Be₂.

[0059] On the other hand, if feedstock powders are mixed together tocontain magnesium, beryllium and boron at a compositional ratio ofMg:Be:B=1:x:y where 0<x<20 and 0<y<20, then there comes out an alloysuperconductor containing the intermetallic compound mentioned above.Here, the compositional ratio can be varied to meet with an applicationpurpose. For example, making Mg larger in compositional proportion mayproduce a superconducting electric cable that especially excels inmalleability and ductility.

[0060] As regards feedstock powders, use may be made of Mg powder or MgOpowder for Mg, Be powder for Be and B or BN powder for B.

[0061] In making an intermetallic-compound superconductor and an alloysuperconductor, several methods are available.

[0062] In a first method, a Mg powder, a Be powder and a B powder aremixed together in an agitating apparatus to form a powder mixture, whichis then shaped into a pellet form, which in turn is heated in an inertgas atmosphere at a temperature of 700 to 2000° C. for a period ofseveral seconds or more by using any known heating means such as archeating, plasma-arc heating or high-frequency melting. This methodpermits forming either superconductor with ease.

[0063] In a second method, a Mg powder, a Be powder and a B powder aremixed together in the agitating apparatus to form a powder mixture,which is then shaped into a pellet form, which in turn is heated in avacuum under a pressure of 2×10⁻² Pa or less at a temperature of 650 to1100° C. for a period of several minutes or more. This method permitsforming either superconductor with ease.

[0064] In a third method, a Mg powder, a Be powder and a B powder aremixed together in the agitating apparatus to form a powder mixture,which is then shaped into a pellet form, which in turn is placed in aHIP (hot isostatic pressing) apparatus (made by, e.g., company KobeSeiko, high temperature, high pressure atmosphere furnace) charged withan inert gas and is heated therein under an inert gas pressure of 1 to200 MPa at a temperature of 600 to 1100° C. for a period of severalminutes or more. This method permits forming either superconductor withease.

[0065] In a fourth method, a Mg powder, a Be powder and a B powder aremixed together in the agitating apparatus to form a powder mixture,which is then shaped into a pellet form, which in turn is placed in acubic anvil pressing or like pressing apparatus and is heated thereinunder a pressure of 0.1 to 6 GPa at a temperature of 700 to 1400° C.(hot pressed) for a period of several minutes or more. This methodpermits forming either superconductor with ease. High pressure isrequired to facilitate joining grain boundaries together while hightemperature is needed to grow superconducting phase.

[0066] It should be noted here that an intermetallic compoundsuperconductor and an alloy superconductor according to the presentinvention are not limited in form to a polycrystalline sintered body asabove but may in form be a polycrystalline bulk body, large singlecrystal, or a thin film.

[0067] Using a conventional bulk body fabricating apparatus such as aforging or a superhigh-pressure pressing and heating synthetic apparatuspermits an intermetallic-compound or alloy superconductor in the form ofa polycrystalline bulk body to be made that is light in weight, high inhardness and excels in corrosion resistance.

[0068] Also, a large single-crystal intermetallic-compound or alloysuperconductor is obtainable by using a known single-crystal growthprocess such as recrystallization, simple lifting, floating zone meltingor fluxing, with the use of a suitable crucible in a controlledatmosphere.

[0069] Further, a thin-film intermetallic-compound or alloysuperconductor is obtainable by chemical gas-phase vapor depositionusing a gas phase source containing magnesium, beryllium and boron atcompositional ratio of Mg:Be:B=1:x:y where 0<x<20 and 0<y<20, or bysputtering with the use of a target material as a sputtering sourcecontaining magnesium, beryllium and boron at the above compositionalratio. Also, for the substrate on which to form a thin-filmintermetallic-compound or alloy superconductor, use may be a metalsubstrate formed of, e.g., Cu, or a ceramic substrate, and may be acomposite substrate having a ceramic deposited on a metal substrate.Such substrates may selectively be used to meet with a particular use orapplication.

[0070] A superconducting alloy that excels in malleability and ductilityis obtainable by making larger the proportion of Mg that excels inmalleability and ductility, or by compounding upon addition of anothermetal or metals that excels in malleability and ductility. Such asuperconducting alloy can be worked by rolling or extrusion into anultra-thin multi-core superconducting cable, a thin superconductingwire, or a superconducting alloy wire or cable.

INDUSTRIAL APPLICABILITY

[0071] As can be appreciated from the foregoing description, the presentinvention provides an intermetallic-compound superconductor made ofmagnesium and beryllium which is high in superconducting transitiontemperature and is easy to make and hence is extremely useful whenapplied to superconducting electronics such as a high performanceJosephson device, a high frequency or electronic device.

[0072] The present invention also provides an alloy superconductor thatcontains the intermetallic compound made of Mg and Be and also containsone or more additional metallic elements, which not only is high insuperconducting transition temperature and excels in malleability andductility, but also is low in specific resistance for normal conduction.Hence, it is not only useful for superconducting electronics such as ahigh performance Josephson device, a high frequency or electronicdevice, but also can highly advantageously be used to formsuperconducting electric cables to make them extremely less costly byeliminating the need to provide current bypassing metal wires therefor.

[0073] Further, using a method as described of making an intermetalliccompound superconductor or an alloy superconductor containing such anintermetallic compound permits the intermetallic superconductor or thealloy superconductor containing such an intermetallic compound to bemanufactured with an extremely high reproducibility, with ease, and at areasonable cost.

What is claimed is:
 1. An intermetallic-compound superconductor,characterized in that it is an intermetallic compound made of magnesium(Mg) and beryllium (Be).
 2. An alloy superconductor, characterized inthat it contains an intermetallic compound made of Mg and Be, and one ormore metallic elements.
 3. An intermetallic-compound superconductor asset forth in claim 1, characterized in that it is of a compositionexpressed by chemical composition formula: Mg₁Be₂ and has a hexagonalAlB₂ type crystallographic structure in which a Mg layer and a Be layerlie alternately.
 4. An alloy superconductor as set forth in claim 2,characterized in that it contains said intermetallic compound and assaid one metallic element boron (B), and is of a composition expressedby chemical composition formula: Mg₁Be_(x)B_(y) where 0<x<20 and 0<y<20.5. An intermetallic-compound superconductor as set forth in claim 1 or3, characterized in that it has a superconducting transition temperature(T_(c)) of 35 K.
 6. An alloy superconductor as set forth in claim 2 or4, characterized in that it has a superconducting transition temperature(T_(c)) of 35 K.
 7. An intermetallic-compound superconductor as setforth in claim 1 or 3, characterized in that it has a specificresistance not greater than 6×10⁻⁵ ohm-cm at a temperature ranging fromits superconducting transition temperature (T_(c)) of 35 K to a roomtemperature.
 8. An alloy superconductor as set forth in claim 2 or 4,characterized in that it has a specific resistance not greater than6×10⁻⁵ ohm-cm at a temperature ranging from its superconductingtransition temperature (T_(c)) of 35 K to a room temperature.
 9. Amethod of making an intermetallic-compound superconductor, characterizedin that it comprises the steps of: mixing a Mg containing feedstockpowder and a Be containing feedstock powder together to form a mixturepowder thereof so that the mixture powder contains Mg and Be at acompositional ratio of Mg/Be=1/2, shaping said mixture powder into theform of a pellet, and heating said pellet in an inert gas to form theintermetallic-compound superconductor.
 10. A method of making anintermetallic compound superconductor, characterized in that itcomprises the steps of: mixing a Mg containing feedstock powder and a Becontaining feedstock powder together to form a mixture powder thereof sothat the mixture powder contains Mg and Be at a compositional ratio ofMg/Be=1/2, shaping said mixture powder into the form of a pellet, andheating said pellet in a vacuum to form the intermetallic compoundsuperconductor.
 11. A method of making an intermetallic compoundsuperconductor, characterized in that it comprises the steps of: mixinga Mg containing feedstock powder and a Be containing feedstock powdertogether to form a mixture powder thereof so that the mixture powdercontains Mg and Be at a compositional ratio of Mg/Be=1/2, shaping saidmixture powder into the form of a pellet, and heating said pellet in apressurized inert gas to form the intermetallic compound superconductor.12. A method of making an intermetallic compound superconductor,characterized in that it comprises the steps of: mixing a Mg containingfeedstock powder and a Be containing feedstock powder together to form amixture powder thereof so that the mixture powder contains Mg and Be ata compositional ratio of Mg/Be=1/2, shaping said mixture powder into theform of a pellet, and pressing and heating said pellet to form theintermetallic compound superconductor.
 13. A method of making an alloysuperconductor, characterized in that it comprises the steps of: mixinga Mg containing feedstock powder, a Be containing feedstock powder and aB containing feedstock powder together to form a mixture powder thereofso that the mixture powder contains Mg, Be and B at a compositionalratio of Mg:Be:B=1:x:y where 0<x<20 and 0<y<20, shaping said mixturepowder into the form of a pellet, and heating said pellet in an inertgas to form the alloy superconductor.
 14. A method of making an alloysuperconductor, characterized in that it comprises the steps of: mixinga Mg containing feedstock powder, a Be containing feedstock powder and aB containing feedstock powder together to form a mixture powder thereofso that the mixture powder contains Mg, Be and B at a compositionalratio of Mg:Be:B=1:x:y where 0<x<20 and 0<y<20, shaping said mixturepowder into the form of a pellet, and heating said pellet in a vacuum toform the alloy superconductor.
 15. A method of making an alloysuperconductor, characterized in that it comprises the steps of: mixinga Mg containing feedstock powder, a Be containing feedstock powder and aB containing feedstock powder together to form a mixture powder thereofso that the mixture powder contains Mg, Be and B at a compositionalratio of Mg:Be:B=1:x:y where 0<x<20 and 0<y<20, shaping said mixturepowder into the form of a pellet, and heating said pellet in apressurized inert gas to form the alloy superconductor.
 16. A method ofmaking an alloy superconductor, characterized in that it comprises thesteps of: mixing a Mg containing feedstock powder, a Be containingfeedstock powder and a B containing feedstock powder together to form amixture powder thereof so that the mixture powder contains Mg, Be and Bat a compositional ratio of Mg:Be:B=1:x:y where 0<x<20 and 0<y<20,shaping said mixture powder into the form of pellet, and pressing andheating said pellet to form the alloy superconductor.
 17. A method ofmaking an intermetallic compound superconductor as set forth in claim 9,characterized in that said pellet is heated in said inert gas at atemperature of 700 to 2000° C. for a period of several seconds or more.18. A method of making an intermetallic compound superconductor as setforth in claim 10, characterized in that said pellet is heated in thevacuum under a pressure of 2×10⁻² Pa or less at a temperature of 650 to1100° C. for a period of several minutes or more.
 19. A method of makingan intermetallic compound superconductor as set forth in claim 11,characterized in that said pellet is heated in said inert gas under apressure of 1 to 200 MPa at a temperature of 600 to 1100° C. for aperiod of several minutes or more.
 20. A method of making anintermetallic compound superconductor as set forth in claim 12,characterized in that said pellet is pressed and heated under a pressureof 0.1 to 6 GPa at a temperature of 700 to 1400° C. for a period ofseveral minutes or more.
 21. A method of making an alloy superconductoras set forth in claim 13, characterized in that said pellet is heated insaid inert gas at a temperature of 700 to 2000° C. for a period ofseveral seconds or more.
 22. A method of making an alloy superconductoras set forth in claim 14, characterized in that said pellet is heated inthe vacuum under a pressure of 2×10⁻² Pa or less at a temperature of 650to 1100° C. for a period of several minutes or more.
 23. A method ofmaking an alloy superconductor as set forth in claim 15, characterizedin that said pellet is heated in said inert gas under a pressure of 1 to200 MPa at a temperature of 600 to 1100° C. for a period of severalminutes or more.
 24. A method of making an alloy superconductor as setforth in claim 16, characterized in that said pellet is pressed andheated under a pressure of 0.1 to 6 GPa at a temperature of 700 to 1400°C. for a period of several minutes or more.